Effects of ankle-to-knee external pressures on skin blood perfusion under and distal to compression.

OBJECTIVE To compare the effects of select leg compression pressures on blood perfusion in the skin overlying bone and the skin distal to the leg compression. DESIGN Blood perfusion of skin overlying the tibia and the foot dorsum was simultaneously measured in 12 healthy subjects using laser Doppler. Each subject's calf was compressed from ankle to knee with an air cast that applied external pressure, ranging from 0 to 40 mm Hg in 10 mm Hg increments. All measurements were initiated after a 20-minute rest interval and were recorded with each subject in a supine position. SETTING University research center. RESULTS The main findings show that compression causes a significant decrease in skin blood perfusion (SBF) at both sites, with greater reductions in SBF occurring with increased compression pressure. Greater SBF reductions occurred at the foot than at the directly compressed tibia site. Thus, at the highest pressure (40 mm Hg), the foot SBF reduction (61.6% +/- 13.7%) was greater than at the directly compressed tibial site (33.3% +/- 0.3%), both of which were significantly less than baseline (P <.01). CONCLUSIONS The present findings and considerable related evidence indicate that lower extremity external compression, within the range of commonly used therapeutic levels, reduces SBF by an amount that depends on the magnitude of the compression pressures. The quantitative difference between the effect of compression on SBF within the compression area, and distal to it, is likely a result of the way that the compression affects arteriolar and venous resistance to blood flow at the 2 sites. From a clinical perspective, it would seem prudent to anticipate that sub-bandage and distal SBF would be negatively affected by compression, with greater effects likely in tissue distal to compression.